Mercury arc



March 6, 1934.

J. MOCULLOUGH MERCURY ARC Filed July 29, 1932 III . 6 g V V 'IIIIIIIIJFII II'IIIIl/IIIA INVENTOR, Ck McCULLOUGH.

A TTORNE Y Patented Mar. 6, 1934 MERCURY ARC Jack McCullough, San Bruno,Calif., assignor to Heintz &"Kaufman, Ltd., San Francisco, Calif., acorporation of Nevada Application July 29, 1932, Serial No. 625,907

3 Claims.

My invention relates to a mercury arc and more particularly to a mercuryarc which is automatically started and maintained even at low currentvalues.

Among the objects of my invention are: To provide an automatic ignitorfor a mercury are operating independently of the arc current; to providea means for maintaining an are at low current densities; to provide astarting device for a mercury are which requires no mechanical shaking;and to provide a simple and inexpensive starting device for a mercuryarc.

Other objects of my invention will be apparent or will be specificallypointed out in the description forming a part of this specification, butI do not limit myself to the embodiment of my invention hereindescribed, as various forms may be adopted within the scope of theclaims.

Referring to the drawing, showing a preferred embodiment of myinvention:

Figure 1 is a longitudinal sectional view indicating the location of theelectrodes.

Figure 2 is a cross sectional view taken in the plane indicated by theline 2-2 in Figure 1.

Figure 3 is a schematic diagram of a circuit in which my tube may beused.

Mercury arcs operating between an anode and a mercury pool cathode willnot start when energized. Various expedients, such as shaking the arc tobreak auxiliary contacts, passing a high frequency spark into the pool,or other devices have been used for starting, the are maintaining itscircuit until the current becomes too low when the arc goes out and mustbe re-started.

In its broadest aspect, my invention comprises a mercury arc tube inwhich there is a mercury pool and an anode energized from a source ofcurrent. Dipping into the surface and making contact with the mercury isan electron-emitting filament, current for which is supplied through themercury from a source operable independently of the anode current flow.The heat of the filament vaporizes mercury at the point of contact,boils it away and breaks the current. This break, combined with theelectrons from the filament starts the are, which is then maintained bythe, anode current. I also prefer to surround the point of filamentcontact with an insulating sleeve, and to provide a shield to preventliquid mercury from splashing on the anode.

Referring to the preferred form shown in the figures, a cylindrical bulb1 is molded with a spherical end 2 and a skirt 4. Fused to the skirt isa reentrant stem 5 having various leads sealed in a pinch 6. The entireenvelope is (c1. re-49 preferably formed from boro-silicate, or otherheat resistant glass. If the device is to be used as a source ofultra-violet light, the container may be of quartz or heat-resistantglasses passing a substantial portion of the ultra-violet spectrum.

A cylindrical anode 7 is welded to an anode lead 9 extending through thepinch, and an anode dummy 10. A relatively large quantity of mercury isinserted in the tube to form a mercury pool 11, to be used as a cathode,and the bulb is placed in an upright position in order that the mercuryremain in the spherical end.

A cathode lead 12 is sealed through the pinch and extended downwardlynear the outer walls of the bulb to pass through the mercury pool andreturn again to the pinch at a dummy insertion 14. This frame providescontact with the mercury pool and also serves to support otherstructures to be described later.

At or near the center of the pinch, an ignitor lead 15 descends towithin a short distance of the surface of the mercury pool, and haswelded to it, as an extension, a filament 16 dipping into and makingcontact with the mercury. This filament is of material capable ofemitting electrons when heated such as solid tungsten, thoriatedtungsten or oxide coated refractory metal.

Welded to the cathode leads 12 between the mercury pool and the anodeare shield supports 17 carrying a shield 19 preferably circular inshape, and having a hole -20 through which the ignitor lead may passwith substantial clearance.

Just below the mercury surface, sleeve supports 21 are welded to thecathode leads 12 and extend inwardly to position a heat-insulatingsleeve 22 of quartz, lavite or like material, by means of a ring band 24frictionally applied to the sleeve. This sleeve extends about half itslength into the mercury, and completely sur- 95 rounds the point ofcontact of the filament 16 with the mercury.

The tube having been assembled as described, is evacuated in an approvedmanner and sealed off the pumps.

Figure 3, a schematic diagram, reduced to its lowest terms, shows onemethod of connection as an are for illumination purposes. Other circuitsmay be employed as when for instance the tube is to be used as arectifier, but the general method 105 of operation will be the sameregardless of use.

The primary 25 of a transformer 26 is energized by alternating currentmains 27. One end of the secondary 29 is directly connected to the anode'7 through the lead 9, the other end con- 110 necting to the filament 16through the ignitor lead 15. The filament circuit is completed byconnection of the mercury pool 11 to a filament section 33 of thetransformer secondary through the lead 12 and a tap 31. The transformersecondary is thus divided into an arc section 32 and the filamentsection 33.

When current is started through the transformer primary, voltage isapplied to the anode and current to the filament passes through themercury. The filament becomes heated, emits electrons, and boils awaythe mercury at the point of contact. This action liberates enoughmercury vapor to be ionized by the emission and the arc strikes betweenthe anode and the surface of the pool.

With sufficient current passing through the arc and consequent heatingof the bulb, to draw down the depth of the pool by evaporation, thecircuit through the filament is broken and will stay broken until thetube should cool down enough to raise the level again to make contact.when contact is made, the filament is heated and electrons and mercuryvapor are again supplied to keep the are alive.

Usually such cooling is due to reduction of current through the arc, andI have found that an are which will not normally operate below- 3amperes, will continue to operate at a current of 1 ampere when theignitor circuit is intermittently making and breaking at the surface ofthe pool. The intermittent action of the ignitor circuit does not seemto unbalance or to modulate the arc current when the arc is operatedbelow 3 amperes.

The insulating sleeve around the point of contact aids in the quickvaporization of mercury at the point of contact, and the shield 19prevents any shorting between anode and cathode due to mercury splashingduring operation.

I have also found it unnecessary to provide the ignitor circuit withcurrent limiting devices or reactances, as the contact of the filamentwith the mercury will be broken by boiling if the filament tends tobecome too hot. It should also be noted that are current will flowirrespective of whether or not the ignitor circuit is open or closed.

Arcs made in accordance with the principles and constrictions describedabove have proved in service to be self-starting without shaking, andthe arc may be maintained by continuous action of the ignitor circuit atcurrent densities which will not maintain a circuit in an ordinary are.

I claim:

1. A mercury arc comprising a cylindrical envelope, a mercury poolcathode in one end of said envelope, a reentrant stem at the oppositeendof said envelope, a rigid conductor sealed through said stem andextending to make permanent contact with said cathode adjacent the wallsof said envelope, a hollow cylindrical anode supported by said stemplaced between said stem and said cathode concentric with the walls ofsaid envelope, a starting electrode extending from said stem throughsaid anode and terminating in an electron emitting tip in contact withthe surface of said cathode, and a cylinder of insulating materialsupported by said rigid conductor surrounding the contact between saidelectron emitting tip and said cathode.

2. A mercury arc comprising a cylindrical envelope, a mercury poolcathode in one end of said envelope, a reentrant stem at the oppositeend of said envelope, a rigid conductor sealed through said stem andextending adjacent one side of said envelope to make contact with saidcathode and returning adjacent the opposite side of said envelope tosaid stem thereby forming a frame, a hollow cylindrical anode supportedby said stem placed between said stem and said cathode concentric withthe walls of said envelope, a starting electrode extending from saidstem through said anode and terminating in an electron emitting tip incontact with the surface of said cathode, and a cylinder of insulatingmaterial supported by said frame surrounding the contact between saidelectron emitting tip and said cathode.

3. A mercury arc comprising a cylindrical envelope, a mercury poolcathode in one end of said envelope, a reentrant stem at the oppositeend of said envelope, a rigid conductor sealed through said stem andextending to makepermanent contact with said cathode adjacent the wallsof said envelope, a hollow cylindrical anode supported by said'stemplaced between said stem and said cathode concentric with the walls ofsaid envelope, 'a starting electrode extending from said stem throughsaid anode and terminating in an electron emitting tip in contact withthe surface of said cathode, a cylinder of insulating material supportedby said rigid conductor surrounding the contact between said electronemitting tip and said cathode, and a circular shield supported by saidrigid conductor placed between said cathode and said anode parallel tothe surface of said cathode, said shield being pierced to allow thepassage of 'said starting electrode therethrough.

, JACK McCULLOUGH.

